Community vulnerability to hazards: introducing local expert knowledge into the equation

The accuracies of three different evolutionary artificial neural network (ANN) approaches, ANN with genetic algorithm (ANN-GA), ANN with particle swarm optimization (ANN-PSO) and ANN with imperialist competitive algorithm (ANN-ICA), were compared in estimating groundwater levels (GWL) based on precipitation, evaporation and previous GWL data. The input combinations determined using auto-, partial auto- and cross-correlation analyses and tried for each model are: (i) GWL _t?1 and GWL _t?2; (ii) GWL _t?1, GWL _t?2 and P _t ; (iii) GWL _t?1, GWL _t?2 and E _t ; (iv) GWL _t?1, GWL _t?2, P _t and E _t ; (v) GWL _t?1, GWL _t?2 and P _t?1 where GWL _t , P _t and E _t indicate the GWL, precipitation and evaporation at time t, individually. The optimal ANN-GA, ANN-PSO and ANN-ICA models were obtained by trying various control parameters. The best accuracies of the ANN-GA, ANN-PSO and ANN-ICA models were obtained from input combination (i). The mean square error accuracies of the ANN-GA and ANN-ICA models were increased by 165 and 124% using ANN-PSO model. The results indicated that the ANN-PSO model performed better than the other models in modeling monthly groundwater levels.     

Salinity Tolerance and Competition Drive Distributions of Native and Invasive Submerged Aquatic Vegetation in the Upper San Francisco Estuary

Both abiotic and biotic factors govern distributions of estuarine vegetation, and experiments can reveal effects of these drivers under current and future conditions. In upper San Francisco Estuary (SFE), increased salinity could result from sea level rise, levee failure, or water management. We used mesocosms to test salinity effects on, as well as competition between, the native Stuckenia pectinata (sago pondweed) and invasive Egeria densa (Brazilian waterweed), species with overlapping distributions at the freshwater transition in SFE. Grown alone at a salinity of 5, E. densa decreased fivefold in biomass relative to the freshwater treatment and decomposed within 3 weeks at higher salinities. In contrast, S. pectinata biomass accumulated greatly (~4× initial) at salinities of 0 and 5, doubled at 10, and was unchanged at 15. When grown together in freshwater, S. pectinata produced 75 % less biomass than in monoculture and significantly more nodal roots (suggesting increased nutrient foraging). At a salinity of 5, a decline in E. densa performance coincided with a doubling of S. pectinata shoot density. Additional experiments on E. densa showed elevated temperature (26 and 30 °C) suppressed growth especially at higher salinities (≥5). We conclude that salinity strongly influences distributions of both species and that competition from E. densa may impose limits on S. pectinata abundance in the fresher reaches of SFE. With a salinity increase of 5, S. pectinata is likely to maintain its current distribution while spreading up-estuary at the expense of E. densa, especially if increased temperature also reduces E. densa biomass.     

Vertical stability and the Brunt-Väisäla frequency of deep natural waters by the example of Lake Baikal,Lake Tanganyika,and the World Ocean

Theoretical analysis, calculations, and comparison with the results of observations in Lake Baikal, Lake Tanganyika, and the World Ocean are performed for the vertical stability E and the Brunt-Väisäla frequency N in the form of N ² with regard to all components (at the constant temperature T and the salinity S, the common adiabatic form at T, S Const). The adiabatic stability E _ad and the Väisäla frequency N in the form of N _ad ² are always positive; at a change from the inverse to the direct temperature stratification, they have deep minimums reaching 10^?16 m^?1 and 10^?15 s^?2 and less; the minimums have the form of a special point, a reversal point of the first kind called a “cusp.” The reality of these reversal points is confirmed by the analysis of the investigation procedure, comparison with the results of previous theoretical (Sherstyankin, et al., 2007), and experimental (observations in Baikal, Shimaraev et al., 1994) works. The features of vertical profiles of E _ad , E andN _ad ² , N ², as well as the layers where the Brunt-Väisäla frequency is less than the inertial frequency, are studied. The analysis with regard to all components of the stability E _ad and the Brunt-Väisäla frequency N makes a great contribution to understanding of mixing processes in theoretical and experimental investigations; it is valid in all reservoirs of the Earth with inverse and direct temperature stratification, including Lake Baikal, Lake Tanganyika, and the World Ocean.     

The potential use of OH-defects in enstatite as geobarometer

In this study, single crystals of pure enstatite (Mg₂Si₂O₆) were synthesised under water-saturated conditions at 4 and 8 GPa and 1,150°C with variable silica activity, leading to phase assemblages enstatite + forsterite, enstatite or enstatite + coesite. Run products were investigated using an FTIR spectrometer equipped with a focal plane array detector enabling IR imaging with a lateral pixel resolution of 2.7 μm. IR spectra within the OH-absorption region show two different groups of absorption bands: group 1 (wavenumbers at 3,592 and 3,687 cm^?1) shows strongest absorptions for E||n _β, whereas group 2 (wavenumbers at 3,067 and 3,362 cm^?1) shows strongest absorptions for E||n _γ. The groups are related to different defect types, group 1 to tetrahedral defects (T-site vacancies) and group 2 to octahedral defects (M-site vacancies). The intensity ratio of the bands within one group (i.e. A ₃₀₆₇/A ₃₃₆₂ and A ₃₅₉₂/A ₃₆₈₇) and the intensity ratio of E||n _γ and E||n _α in group 2 bands remain constant within error. In contrast, the intensity ratio of group 2 to group 1 absorption bands [e.g. (A ₃₃₆₂)/(A ₃₆₈₇)] is sensitive to the SiO₂ activity and pressure. On the basis of the results of this and previous studies, a barometer for pure orthoenstatite coexisting with forsterite can be formulated:\( P\,[{\text{GPa}}] = 1.056 + \sqrt {{\frac{{1.025 - A_{{\left( {3362} \right)/\left[ {(3362) + (3687)} \right]}} }}{0.009}}} , \) where A ₍₃₃₆₂₎ and A ₍₃₆₈₇₎ are the integral absorbances of the component E||n _γ of the absorption bands at 3,362 cm^?1 and the component E||n _β of the absorption band at 3,687 cm^?1, respectively.     

Middle Pleistocene-Holocene calcareous plankton and benthos biostratigraphy of the Markova Depression,equatorial atlantic

The analysis of nannoplankton, planktonic and benthic foraminifer assemblages provided detailed biostratigraphic characteristics of the upper part of sedimentary cover in the Markova Depression, rift valley of the Mid-Atlantic Ridge. The Gephyrocapsa oceanica and Emiliania huxleyi nannofossil zones, (LO) Helicosphaera inversa biohorizon, Emiliania huxleyi Acme Zone, and planktonic foraminiferal Globigerina calida calida, Globigerina bermudezi and Globorotalia fimbriata subzones were recognized. The compiled paleotemperature curve is correlated with the upper 10 oxygen isotope stages. The recovered deposits were accumulated during 400 ka. Changes in abundance and species composition of benthic foraminifer assemblages are suggested to be correlative with hydrothermal activity outbreaks in the rift zone.     

Argon retention properties of silicate glasses and implications for <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar age and noble gas diffusion studies

Sized aggregates of glasses (47–84 wt% SiO₂) were fused from igneous-derived cohesive fault rock and igneous rock, and step-heated from ~400 to >1,200 °C to obtain their ³⁹Ar diffusion properties (average E=33,400 cal mol^?1; D _o=4.63×10^?3 cm² s^?1). At T<~1,000 °C, glasses containing <~69 wt% SiO₂ and abundant network-forming cations (Ca, Fe, Mg) reveal moderate to strong non-linear increases in D and E, reflecting structural modifications as the solid transitions to melt. Extrapolation of these Arrhenius properties down to typical geologic T-t conditions could result in a 1.5 log₁₀ unit underestimation in the diffusion rate of Ar in similar materials. Numerical simulations based upon the diffusion results caution that some common geologic glasses will likely yield ⁴⁰Ar/³⁹Ar cooling ages rather than formation ages. However, if cooling rates are sufficiently high, ambient temperatures are sufficiently low (e.g., <65–175 °C), and coarse particles (e.g., radius (r) >~1 mm) are analyzed, glasses with compositions similar to ours may preserve their formation ages.     

Stable carbon and oxygen isotope study on benthic foraminifera: Implication for microhabitat preferences and interspecies correlation

Stable isotopes of benthic foraminifera have widely been applied in micropalaeontological research to understand vital effects in foraminifera. Isotopic fractionations are mainly controlled by ontogeny, bottom/pore water chemistry, habitat preference, kinetic effect and respiration. Discontinuous abundance of a species for isotopic analysis has forced us to select multiple species from down-core samples. Thus standardisation factors are required to convert isotopic values of one species with respect to other species. The present study is pursued on isotopic values of different pairs of benthic foraminifera from the Krishna–Godavari basin and Peru offshore to understand habitat-wise isotopic variation and estimation of isotopic correction factors for the paired species (Cibicides wuellerstorfi–Bulimina marginata, Ammonia spp.–Loxostomum amygdalaeformis and Bolivina seminuda–Nonionella auris). Infaunal species (B. marginata, Ammonia spp. and N. auris) show a lighter carbon isotopic excursion with respect to the epifaunal to shallow infaunal forms (C. wuellerstorfi, L. amygdalaeformis and B. seminuda). These lighter \(\updelta ^{13}\) \(\hbox {C}\) values are related to utilisation of \(\hbox {CO}_{2}\) produced by anaerobic remineralisation of organic matter. However, enrichment of \(\updelta ^{18}\) \(\hbox {O}\) for the deeper microhabitat (bearing lower pH and decreased \({\hbox {CO}_{3}}^{2-})\) is only recorded in case of B. marginata. It is reverse in case of N. auris and related to utilisation of respiratory \(\hbox {CO}_{2}\) and internal dissolve inorganic carbon pool. Estimation of interspecies isotopic correction factors for the species pairs (\(\updelta ^{13}\) \(\hbox {C}\) of C. wuellerstorfi–B. marginata, L. amygdalaeformis–Ammonia spp., N. auris–B. seminuda) and \(\updelta ^{18}\) \(\hbox {O}\) of C. wuellerstorfi–B. marginata are statistically reliable and may be used in palaeoecological studies.     

Analytical methods for measuring the parameters of interstellar gas using methanol observations

The excitation of methanol in the absence of external radiation is analyzed, and LTE methods for probing interstellar gas considered. It is shown that rotation diagrams correctly estimate the gas kinetic temperature only if they are constructed using lines whose upper levels are located in the same K-ladders, such as the J₀?J_?1E lines at 157 GHz, the J₁?J₀E lines at 165 GHz, and the J₂?J₁E lines at 25 GHz. The gas density must be no less than 10⁷ cm^?3. Rotation diagrams constructed from lines with different K values for their upper levels (e.g., 2_K?1_K at 96 GHz, 3_K?2_K at 145 GHz, 5_K?4_K at 241 GHz) significantly underestimate the temperature, but enable estimation of the density. In addition, diagrams based on the 2_K?1_K lines can be used to estimate the methanol column density within a factor of about two to five. It is suggested that rotation diagrams should be used in the following manner. First, two rotation diagrams should be constructed, one from the lines at 96, 145, or 241 GHz, and another from the lines at 157, 165, or 25 GHz. The former diagram is used to estimate the gas density. If the density is about 10⁷ cm^?3 or higher, the latter diagram reproduces the temperature fairly well. If the density is around 10⁶ cm^?3, the temperature obtained from the latter diagram should be multiplied by a factor of 1.5–2. If the density is about 10⁵ cm^?3 or lower, then the latter diagram yields a temperature that is lower than the kinetic temperature by a factor of three or more, and should be used only as a lower limit for the kinetic temperature. The errors in the methanol column density determined from the integrated intensity of a single line can be more than an order of magnitude, even when the gas temperature is well known. However, if the J₀?(J ? 1)₀E lines, as well as the J₁?(J ? 1)₁A⁺ or A^? lines are used, the relative error in the column density is no more than a factor of a few.     

Occurrence of selected volatile organic compounds in a bra cup manufacturing facility

This article presents a review of the types and levels of volatile organic compounds (VOC) detected in a bra cup manufacturing facility (considering the past 4 years) while conducting a human health risk assessment to selected VOCs. Most of the tested VOCs were undetected, except in the flocking section in 2014. However, from time to time dichloromethane and toluene were detected in the facility. Dichloromethane levels showed an increase with time in the laminating section (except during 2014) with drastically higher levels in 2015. SWIFT VS1 6016/5A (an adhesive) as per the material safety data sheet (MSDS) was the dichloromethane source. However, none of the MSDS revealed the occurrence of carcinogenic benzene (which was detected in 2014 in the flocking section) and 1,4-dichlorobenzene (which was detected in 2013 in the laminating and injection molding sections) and non-carcinogenic toluene indicating that MSDS do not accurately provide the identity of chemicals. Hazard Indices (HI) for non-carcinogenic VOCs and the total lifetime cancer risks (LCRs) and occupational exposure indices (E _i ) for carcinogenic VOCs varied during the different time periods. Toluene in many cases accounted for 100 % of the HI. LCRs and E _i of dichloromethane accounted for 100 % of the total LCR and total E _i , respectively (except in the flocking section in 2014). LCR and E _i of the individual VOCs (even the total LCR and E _i values) were simultaneously high whenever the levels of the individual VOCs had exceeded the regulatory limits posing a health risk. Some measures needed to prevent exposure to VOCs are discussed in this article.     

Seasonal Factors Influencing Copepod Abundance in the Maryland Coastal Bays

Maryland Coastal Bays differ in hydrography from river-dominated estuaries because of limited freshwater inflow from tributary creeks and more marine influence. Consequently, the copepod community structure may be different from that of the coastal ocean and river-dominated estuaries in the mid-Atlantic region. A 2-year study was conducted to describe copepod species composition and seasonal patterns in abundance and factors influencing the community structure. Seven copepod genera, Acartia, Centropages, Pseudodiaptomus, Parvocalanus, Eurytemora, Oithona, and Temora, in addition to harpacticoids were found. The copepod community was dominated by Acartia spp. (64%), followed by Centropages spp. (30%), unlike in river-dominated estuaries in the region where the copepod community is usually dominated by Acartia spp. followed by Eurytemora affinis. Acartia tonsa was the most abundant in summer and fall whereas Centropages spp., Temora sp., Oithona similis, E. affinis, and harpacticoids were most abundant in winter and early spring. Parvocalanus crassirostris and Pseudodiaptomus pelagicus were present in fall and winter but at relatively low densities. The highest mean density of copepods occurred in winter 2012 (36,437 m^?3) and the lowest in spring 2013 (347 m^?3). Low densities occurred through early summer (614 m^?3) coinciding with peak spawning by bay anchovy (Anchoa mitchilli). Bottom-up control via low phytoplankton biomass coupled with top-down control by ctenophores (Mnemiopsis sp.), mysids (Neomysis americana), and bay anchovy was probably responsible for the low copepod densities in spring and early summer. Temperature and salinity were also important factors that influenced the seasonal patterns of copepod species occurrence. The observed seasonal differences in the abundance of copepods have important implications for planktivorous fishes as they may experience lower growth rates and survival due to food limitation in spring/early summer when copepod densities are relatively low than in late summer/fall when copepod abundance is higher.     

Modelling the effects of porous media deformation on the propagation of water-table waves in a sandy unconfined aquifer

This paper examines the influence of porous media deformation on water-table wave dispersion in an unconfined aquifer using a numerical model which couples Richards’ equation to the poro-elastic model. The study was motivated by the findings of Shoushtari et al. (J Hydrol 533:412–440, 2016) who were unable to reproduce the observed wave dispersion in their sand flume data with either numerical Richards’ equation models (assuming rigid porous media) or existing analytic solutions. The water-table wave dispersion is quantified via the complex wave number extracted from the predicted amplitude and phase profiles. A sensitivity analysis was performed to establish the influence of the main parameters in the poro-elastic model, namely Young’s modulus (E) and Poisson’s ratio (ν). For a short oscillation period (T?=?16.4 s), the phase lag increase rate (k _i) is sensitive to the chosen values of E and ν, demonstrating an inverse relationship with both parameters. Changes in the amplitude decay rate (k _r), however, were negligible. For a longer oscillation period (T?=?908.6 s), variations in the values of E and ν resulted in only small changes in both k _r and k _i. In both the short and long period cases, the poro-elastic model is unable to reproduce the observed wave dispersion in the existing laboratory data. Hence porous media deformation cannot explain the additional energy dissipation in the laboratory data. Shoushtari SMH, Cartwright N, Perrochet P, Nielsen P (2016) The effects of oscillation period on groundwater wave dispersion in a sandy unconfined aquifer: sand flume experiments and modelling. J Hydrol 533:412–440.     

Is NGC 7006 a globular cluster with a primarily red horizontal branch?

A CCD BV R photometric study of the central region (15″ ≤ r ≤ 100″) of the globular cluster NGC 7006 based on color-magnitude diagrams is presented. We find for the main parameters of the cluster [Fe/H] = ?1.62, Y = 0.21, E _B?V = 0.15 ^m , V _HB = 18.84 ^m , M _V ^HB =+0.56 ^m , R _⊙ = 37.1 kpc). Two previously unknown RR Lyr variables were discovered in the central region of the cluster. The morphological index of the horizontal branch for the entire region studied indicates that the red stellar population dominates, consistent with previous studies: HB _mi = ?0.13. Such anomalously negative morphological indices are possessed by a whole group of Ool clusters with intermediate metallicities, which also display a characteristic distribution of stars along the horizontal branch. There is a radial dependence for the horizontal-branch morphology, with the color becoming primarily blue with approach toward the cluster center. One possible origin for this behavior could be the effect of inner dynamical processes on the spatial distribution of hot stars.     

Biostratigraphy of the Çeşmeler and Elmalι Dere formations: First records of upper Cretaceous planktonic foraminifera and radiolarians from the Eastern Pontides (Maçka,Trabzon, Turkey)

Upper Cretaceous pelagic deposits outcropping in the Maçka (Trabzon) region include radiolarians and pelagic foraminifera. The Çatak Group represented by the volcano-sedimentary successions consists of three formations having different properties. Two sections, ÇTK1 and ÇTK2, are selected from the Çe meler and Elmalι Dere formations, respectively, establishing the biostratigraphy of outcropping sedimentary units. A total of 17 species of Whiteinella, Helvetoglobotruncana, Marginotruncana, Dicarinella, Praeglobotruncana, Archaeoglobigerina and Hedbergella demonstrating the early Turonian–Coniacian are established in the ÇTK1 stratigraphic section. The early Turonian radiolarian fauna consisting of Halesium sexangulum Pessagno, 1971, Crucella cachensis Pessagno, 1971, Stichomitra communis Squinabol, 1903 is also defined in the same section. A total of 30 species of Crucella, Halesium, Pessagnobrachia, Patulibracchium, Alievium, Archaeospongoprunum, Dicyomitra, Stichomitra, Diacanthocapsa, Dactiyliodiscus, Amphipydax, Pseudoaulophocus, Acaeniotyle, Archaeodictyomitra, Actinomma, Xitus, Neosciadocapsidae characterizing the early and late Turonian, as well as the Coniacian–early Santonian are recognized from red-coloured pelagic limestones of the ÇTK2 section. Also, planktonic foraminifera species of Marginotruncana, Hedbergella, Heterohelix, Globotruncana, Globotruncanita, Archaeoglobigerina, Dicarinella characterizing the Coniacian–Santonian are described in the thin sections of the same samples. The age of red-coloured limestones is identified as the Coniacian–Santonian benefit from radiolarians and pelagic foraminifera. Consequently, radiolarians and pelagic foraminifera within sedimentary successions of the investigation area are distributed in two intervals that coincide with the early Turonian–Coniacian and Coniacian–Santonian intervals.     

Refinement of stratigraphy according to the first finds of planktonic species of <Emphasis Type="Italic">Orbulina</Emphasis> and <Emphasis Type="Italic">Praeorbulina</Emphasis> from the Guri Limestone of the Mishan Formation in northwest of Bandar Abbas,South Iran

The Zagros Basin is one of the most universal oil and gas basins that is located in the west to south of Iran and in north of the Arabian Plate. The Guri Member at the bottom of the Mishan Formation, in some areas such as Bandar Abbas hinterland, contains a significant amount of gas. The Bandar Abbas hinterland is located in the southeast of Zagros. The Guri Limestone is the youngest hydrocarbon reservoirs of the Zagros Sedimentary Basin. In this study, a total of 178 samples from the Guri Limestone in the Handun section are investigated for foraminiferal biostratigraphy. The study of foraminifers led to a recognition of 43 genera and 57 species of benthic and planktonic foraminifera. For the first time, planktonic foraminiferal species including Praeorbulina glomerosa, Praeorbulina transitoria, Orbulina suturalis, and Orbulina universa are reported, and based on the identified benthic and planktonic foraminifera taxa, the age of the Guri Member at Handun section is estimated as late Burdigalian to Langhian.     

The gas density and “volume” Schmidt law for spiral galaxies

The equilibrium thickness of the isothermal layers of interstellar gas and volume gas densities ρ _gas in the plane of the disk as a function of galactocentric distance R are computed for seven spiral galaxies (including the Milky Way) using an axisymmetrical model. In this model, the thickness of the stellar disk varies with R and remains approximately equal to the minimum thickness of a stable equilibrium disk. We found the disk thickness to increase toward the periphery in at least five of the seven galaxies. The density of the stellar disk decreases with R faster than ρ _gas , so that gas dominates at the disk peripheries in terms of density. A comparison of the azimuthally averaged star formation rate SFR and the gas density shows the absence of a universal Schmidt law SFR ～ρ _gas ⁿ for galaxies. However, the SFRs in various galaxies are better correlated with the volume than the gas surface density. The parameter n in the Schmidt law formally calculated using the least-squares method lies in the interval 0.8–2.4, being, on average, close to 1.5. The values of n calculated separately for the molecular gas display substantial scatter, but are, on average, close to unity. The value of n appears to increase with decreasing ρ _gas , so that the fraction of gas that actively participates in star formation decreases with n.     

The mass of the compact object in the X-ray binary her X-1/HZ her

We have obtained the first estimates of the masses of the components of the Her X-1/HZ Her X-ray binary system taking into account non-LTE effects in the formation of the H _γ absorption line: m _x = 1.8 M _⊙ and m _v = 2.5 M _⊙. These mass estimates were made in a Roche model based on the observed radial-velocity curve of the optical star, HZ Her. The masses for the X-ray pulsar and optical star obtained for an LTE model lie are m _x = 0.85 ± 0.15 M _⊙ and m _v = 1.87 ± 0.13 M _⊙. These mass estimates for the components of Her X-1/HZ Her derived from the radial-velocity curve should be considered tentative. Further mass estimates from high-precision observations of the orbital variability of the absorption profiles in a non-LTE model for the atmosphere of the optical component should be made.     

Masses of the visual components and black holes in X-ray novae: Effects of proximity of the components

It is shown that the approximation of the complex, tidally distorted shape of a star as a circular disc with local line profiles and a linear limb-darkening law, which is usually applied when deriving equatorial stellar rotation velocities from line profiles, leads to overestimation of the equatorial velocity V _rot sin i and underestimation of the component mass ratio q = M _x /M _v . A formula enabling correction of the effect of these simplifying assumptions on the shape of a star is used to re-determine the mass ratios q and the masses of the black holes M _x and visual components M _v in low-mass X-ray binary systems containing black holes. Taking into account the tidal–rotational distortion of the stellar shape can significantly increase the mass ratios q = M _x /M _v , reducing M _v , while M _x changes only slightly. The resulting distribution of M _v attains its maximum near M _v ? 0.35M _⊙, in disagreement with the results of population synthesis computations realizing standard models for Galactic X-ray novae with black holes. Possible ways to overcome this inconsistency are discussed. The derived distribution of M _x also differs strongly from the mass distribution for massive stars in the Galaxy.     

Timescales for mechanisms for the dynamical evolution of open star clusters

We have obtained the stellar velocity dispersion in three mutually perpendicular directions in the halos and cores of clusters as a function of time for several non-stationary open-cluster models. During the dynamical evolution of the open-cluster models, the velocity dispersions undergo oscillations that do not decay during 5–10 violent-relaxation timescales, τ _vr . We estimated the time for synchronization of the rotation of the open-cluster models and their motion around the center of the Galaxy, t _s , which, depending on the model parameters, is t _s ? (5–27)τ _vr . Synchronization mechanisms for the models are discussed. The disruption of the systems in the force field of the Galaxy is strongly affected by tidal friction. We have also estimated the time for the formation of a spherical stellar-velocity distribution in the cluster models, t _σ ? (6 ? 25)τ _vr . The impact of instability in the stellar motions in a cluster on the formation of a spherical velocity distribution in the open-cluster models is discussed. We have noted a tendency for a weakening of the dependence of the coarse phase density of the cluster on small initial perturbations of the stellar phase coordinates in the model cluster cores for times about five times longer than the violent-relaxation time.     

The evolution of hydrocarbon dust grains in the interstellar medium and its influence on the infrared spectra of dust

Computations of the evolution of the distributions of the size and degree of aromatization of interstellar dust grains, destruction by radiation and collisions with gas particles, and fragmentation during collisions with other grains are presented. The results of these computations are used to model dust emission spectra. The evolution of an ensemble of dust particles sensitively depends on the initial size distribution of the grains. Radiation in the considered range of fluxes mainly aromatizes grains. With the exception of the smallest grains, it is mainly erosion during collisions with gas particles that leads to the destruction of grains. In the presence of particle velocities above 50 km/s, characteristic for shocks in supernova remnants, grains greater than 20 Å in size are absent. The IR emission spectrum changes appreciably during the evolution of the dust, and depends on the adopted characteristics of the grains, in particular, the energy of their C–Cbonds (E₀). Aromatic bands are not observed in the near-IR (2–15 μm) when E₀ is low, even when the medium characteristics are typical for the average interstellarmedium in our Galaxy; this indicates a preference for high E₀ values. The influence of the characteristics of the medium on the intensity ratios for the dust emission in various photometric bands is considered. The I_3.4/I_11.3 intensity ratio is most sensitive to the degree of aromatization of small grains. The I_3.3/I₇₀₊₁₆₀ ratio is a sensitive indicator of the contribution of aromatic grains to the total mass of dust.